H2 Plasma and PMA Effects on PEALD-Al2O3 Films with Different O2 Plasma Exposure Times for CIS Passivation Layers

In this study, the electrical properties of Al2O3 film were analyzed and optimized to improve the properties of the passivation layer of CMOS image sensors (CISs). During Al2O3 deposition processing, the O2 plasma exposure time was adjusted, and H2 plasma treatment as well as post-metallization annealing (PMA) were performed as posttreatments. The flat-band voltage (Vfb) was significantly shifted (ΔVfb = 2.54 V) in the case of the Al2O3 film with a shorter O2 plasma exposure time; however, with a longer O2 plasma exposure time, Vfb was slightly shifted (ΔVfb = 0.61 V) owing to the reduction in the carbon impurity content. Additionally, the as-deposited Al2O3 sample with a shorter O2 plasma exposure time had a larger number of interface traps (interface trap density, Dit = 8.98 × 1013 eV−1·cm−2). However, Dit was reduced to 1.12 × 1012 eV−1·cm−2 by increasing the O2 plasma exposure time and further reduced after PMA. Consequently, we fabricated an Al2O3 film suitable for application as a CIS passivation layer with a reduced number of interface traps. However, the Al2O3 film with increased O2 plasma exposure time deteriorated owing to plasma damage after H2 plasma treatment, which is a method of reducing carbon impurity content. This deterioration was validated using the C–V hump and breakdown characteristics.


Introduction
Recently, the importance of CMOS image sensor (CIS) technology has rapidly increased owing to its relevance in mobile products and autonomous driving. As electronic products become ever-smaller in size, smaller CIS devices are also required. Therefore, CIS devices must be scaled, similar to other semiconductor devices. The pixel size of the CIS image sensor has been rapidly scaled, limiting the number of photons entering the pixel. In addition, as a result of scaling, light reflection occurred, causing light loss and cross-talk issues [1]. Therefore, a backside illumination-type CIS device that illuminates the rear side of the device was developed [2]. However, the backside illumination structure is adversely affected by dark currents and noise. Hence, in order to decrease dark current and increase quantum efficiency, research on the development of high-k materials for application as a CIS passivation dielectric layer is necessary. Al 2 O 3 , which is a high-k dielectric material, has a wide energy bandgap and high thermal stability; therefore, it is suitable for application as a passivation dielectric film for CIS [3,4]. In addition, unlike other dielectric films, Al 2 O 3 has negative fixed charges and shows excellent passivation characteristics [5]. In most semiconductor devices such as complementary metal oxide semiconductors (CMOSs), fixed charges act as defects [6]. Thus, many studies have been conducted to control these negative fixed charges [7]. However, in the CIS device, a passivation dielectric layer is required to contain high fixed charges for field effect passivation. Therefore, Al 2 O 3 is a suitable dielectric material as a passivation layer of CIS. However, a dielectric film with fewer impurities is required for fabricating a more precise CIS device, and defects in Al 2 O 3 must be further cured. In particular, for application as a dielectric film, the interface trap density (D it ) should be reduced to increase the amount of light absorbed. There are several causes of trap generation in the interface area between Al 2 O 3 dielectric and substrate. If the Al 2 O 3 dielectric is deposited on the silicon substrate, the hydroxyl group (-OH) and Si are bonded, which may act as an interface trap [8]. In another case, carbon impurities generated during the Al 2 O 3 deposition process act as interface traps.
Carbon impurities were generated after the Al 2 O 3 film was deposited via plasmaenhanced atomic layer deposition (PEALD) using trimethylaluminum as a precursor [9]. These impurities act as traps inside the Al 2 O 3 and in the interface region. Previously, residual carbon was removed using the H 2 plasma treatment of an Al 2 O 3 film [10]. The quality of the dielectric and interface areas increased with a decrease in carbon impurity contents. In addition, posttreatments provided sufficient fixed charges for the Al 2 O 3 dielectric to be used as the passivation layer of the CIS [11,12]. However, a low D it is required for next-generation CIS devices. Although well-known defects, such as oxygen vacancies, have been investigated [13], limited studies have been conducted to reduce residual carbon contents, except by changing the precursor [14].
In this study, the oxygen plasma exposure time was adjusted during Al 2 O 3 deposition to reduce the residual carbon content. The increased O 2 plasma exposure time sufficiently decreased the D it of the Al 2 O 3 gate stack. Consequently, it showed a considerably lower D it compared with that of the sample processed via rapid thermal annealing and H 2 plasma treatment on Al 2 O 3 , which exhibited the lowest D it in a previous study [10]. In particular, D it was the lowest after post-metallization annealing (PMA) to Al 2 O 3 samples with increased O 2 plasma exposure time. In addition, a positive shift in flat-band voltage (∆V fb ) was prevented by reducing carbon generation. However, D it increases when H 2 plasma treatment is performed after Al 2 O 3 deposition. Plasma damage and residual hydrogen impurities were caused by excessive H 2 plasma treatment on Al 2 O 3 dielectric and were validated using the C-V hump occurring in the capacitance vs. voltage (C-V G ) measurement curve.

Experimental Materials and Methods
As shown in Figure 1, an Al 2 O 3 film was deposited on a Si substrate at 275 • C using PEALD. Substrate included moderately doped p-type Si (1-30 Ω·cm, (100)) with a doping concentration of~1.3 × 10 16  . Under the N 2 gas flow, the temperature increased from 25 • C to 400 • C in 1 h and then decreased from 400 • C to 25 • C in 2 h. Secondary ion mass spectrometry (SIMS) measurements were conducted on a circular area with a diameter of 33 µm using the Cs+ software. Selective area diffraction pattern (SADP) analysis was carried out to determine crystallinity of the Al 2 O 3 film. The capacitance and conductance were measured using a B1520A multifrequency capacitance measurement unit at various frequencies (1 kHz-1 MHz). The leakage current and breakdown field were measured using a Keithley 4200-SCS instrument (Tektronix KOREA, Seoul, Republic of Korea). D it (≈2.5(qA) −1 (G p /ω) max ) was calculated following the well-known conductance method [15]: where q = 1.6 × 10 19 C; A is the area of the electrode; (G p /ω) max is the normalized parallel conductance peak; C OX is the capacitance in strong accumulation; C M is the measured capacitance; and G M is the measured conductance.  25 °C in 2 h. Secondary ion mass spectrometry (SIMS) measurements were conducted on a circular area with a diameter of 33 µm using the Cs+ software. Selective area diffraction pattern (SADP) analysis was carried out to determine crystallinity of the Al2O3 film. The capacitance and conductance were measured using a B1520A multifrequency capacitance measurement unit at various frequencies (1 kHz-1 MHz). The leakage current and breakdown field were measured using a Keithley 4200-SCS instrument (Tektronix KOREA, Seoul, KOREA). Dit (≈2.5(qA) −1 ( / )max) was calculated following the well-known conductance method [15]: where q = 1.6 × 10 19 C; A is the area of the electrode; ( / )max is the normalized parallel conductance peak; is the capacitance in strong accumulation; is the measured capacitance; and is the measured conductance.

Post-Metallization Annealing
Al2O3 was deposited via PEALD using trimethylaluminum as the precursor and O2 plasma. A flux of O* radicals reacts with methyl groups and is effused in the COX (x = 1-2) state [16]. However, residual carbon is generated when a sufficient reaction is not performed and acts as a defect in the inner and interfacial regions of Al2O3. Accordingly, the O2 plasma exposure time was increased to 7 s to ensure a sufficient response.

Post-Metallization Annealing
Al 2 O 3 was deposited via PEALD using trimethylaluminum as the precursor and O 2 plasma. A flux of O* radicals reacts with methyl groups and is effused in the CO X (x = 1-2) state [16]. However, residual carbon is generated when a sufficient reaction is not performed and acts as a defect in the inner and interfacial regions of Al 2 O 3 . Accordingly, the O 2 plasma exposure time was increased to 7 s to ensure a sufficient response.
The TEM image of the as-deposited Al 2 O 3 film is shown in Figure 2a. An Al 2 O 3 film with a thickness of 30 nm was deposited on the Si substrate, and Al electrode was deposited on the Al 2 O 3 dielectric. No interfacial layer (IL) was formed at the interface between Si and Al 2 O 3 . Additionally, based on the SADP in Figure 2a, the as-deposited Al 2 O 3 is in an amorphous state. Nanomaterials 2023, 13,731 The TEM image of the as-deposited Al2O3 film is shown in Figure 2a. An Al2O with a thickness of 30 nm was deposited on the Si substrate, and Al electrode was d ited on the Al2O3 dielectric. No interfacial layer (IL) was formed at the interface be Si and Al2O3. Additionally, based on the SADP in Figure 2a, the as-deposited Al2O an amorphous state. PMA was performed at 400 °C for 30 min after Al2O3 film deposition. After PM the Al2O3 film, oxygen in the dielectric film diffused toward the Si substrate. Accord Si and oxygen form a bond in the SiOX (x = 1-2) state, thereby forming an IL with a ness of 2.5 nm [8,17] (Figure 2b). As IL was formed between Al2O3 and Si, the thickn Al2O3 decreased from 28.7 to 26.9 nm after PMA. Furthermore, as shown in SADP, phous Al2O3 is converted to polycrystalline Al2O3 via PMA [18].
The normalized capacitance vs. voltage curves before and after PMA of S1 and shown in Figure 3. The graphical ((COX/CMOS) 2 − 1)(VG) method [19] was applied normalized capacitance vs. voltage curve to extract Vfb. The Vfb of as-deposited S 1.65 V, showing a considerable flat-band voltage shift (∆Vfb ≈ 2.54 V) compared w theoretical value of Al2O3 dielectric (Vfb ≈ −0.89 V). This Vfb shift resulted from d such as carbon impurities that occur during Al2O3 deposition via PEALD. However case of S2 samples with an increased O2 plasma exposure time, the Vfb of S2_as_dep V, exhibiting a smaller ∆Vfb compared with that of S1. This is because the amount o atively charged defects inside S2 is smaller than that of S1. PMA was performed at 400 • C for 30 min after Al 2 O 3 film deposition. After PMA on the Al 2 O 3 film, oxygen in the dielectric film diffused toward the Si substrate. Accordingly, Si and oxygen form a bond in the SiO X (x = 1-2) state, thereby forming an IL with a thickness of 2.5 nm [8,17] (Figure 2b). As IL was formed between Al 2 O 3 and Si, the thickness of Al 2 O 3 decreased from 28.7 to 26.9 nm after PMA. Furthermore, as shown in SADP, amorphous Al 2 O 3 is converted to polycrystalline Al 2 O 3 via PMA [18].
The normalized capacitance vs. voltage curves before and after PMA of S1 and S2 are shown in Figure 3. The graphical ((C OX /C MOS ) 2 − 1)(V G ) method [19] was applied to the normalized capacitance vs. voltage curve to extract V fb . The V fb of as-deposited S1 was 1.65 V, showing a considerable flat-band voltage shift (∆V fb ≈ 2.54 V) compared with the theoretical value of Al 2 O 3 dielectric (V fb ≈ −0.89 V). This V fb shift resulted from defects, such as carbon impurities that occur during Al 2 O 3 deposition via PEALD. However, in the case of S2 samples with an increased O 2 plasma exposure time, the V fb of S2_as_dep is 0.61 V, exhibiting a smaller ∆V fb compared with that of S1. This is because the amount of negatively charged defects inside S2 is smaller than that of S1. Vfb increased by 0.54 V after PMA in the case of Al2O3 samples with short O2 plasma exposure times. Internal defects that form bonds with carbon impurities have a negative charge and diffuse toward Si [10,14]. However, in the case of S2 samples with long O2 plasma exposure times, the change in Vfb was as small as 0.2 V owing to a decrease in the   [10,14]. However, in the case of S2 samples with long O 2 plasma exposure times, the change in V fb was as small as 0.2 V owing to a decrease in the defects that can be diffused.
The permittivity of Al 2 O 3 samples before and after PMA is shown in Figure 4. The permittivity is 9.5 in the case of the as-deposited S1 sample, which is similar to the generally known permittivity value of amorphous Al 2 O 3 (6-9) [18,20]. However, an IL of SiO X (x = 1-2) is formed between Al 2 O 3 and Si after PMA, slightly decreasing the permittivity. The permittivity of the as-deposited S2 sample is 12.5, which is considerably higher than that of the S1 sample. This is because of the decrease in the content of various defects and the increase in the internal carbon concentration owing to the longer O 2 plasma exposure time. After PMA on the as-deposited S2 sample, the permittivity decreases to 10.5 because an IL of SiOx (x = 1-2) is formed between Al 2 O 3 and Si like the S1 sample. However, the S2_PMA sample still showed a higher permittivity than the S1 samples with shorter O 2 plasma exposure time. Vfb increased by 0.54 V after PMA in the case of Al2O3 samples with short O2 plasma exposure times. Internal defects that form bonds with carbon impurities have a negative charge and diffuse toward Si [10,14]. However, in the case of S2 samples with long O2 plasma exposure times, the change in Vfb was as small as 0.2 V owing to a decrease in the defects that can be diffused.
The permittivity of Al2O3 samples before and after PMA is shown in Figure 4. The permittivity is 9.5 in the case of the as-deposited S1 sample, which is similar to the generally known permittivity value of amorphous Al2O3 (6-9) [18,20]. However, an IL of SiOX (x = 1-2) is formed between Al2O3 and Si after PMA, slightly decreasing the permittivity. The permittivity of the as-deposited S2 sample is 12.5, which is considerably higher than that of the S1 sample. This is because of the decrease in the content of various defects and the increase in the internal carbon concentration owing to the longer O2 plasma exposure time. After PMA on the as-deposited S2 sample, the permittivity decreases to 10.5 because an IL of SiOx (x = 1-2) is formed between Al2O3 and Si like the S1 sample. However, the S2_PMA sample still showed a higher permittivity than the S1 samples with shorter O2 plasma exposure time.  The decrease in the carbon impurity content with increasing O 2 plasma exposure time was validated using SIMS depth profiling. As shown in Figure 5, the amount of carbon impurities in the Al 2 O 3 film deposited with an O 2 plasma exposure time of 7 s is considerably less than that of the Al 2 O 3 sample deposited with a shorter O 2 plasma exposure time. As the O 2 plasma exposure time increased, more carbon was effused into the CO X (x = 1-2) gas state through numerous reactions between the oxygen plasma and carbon [16]. If the O 2 plasma exposure time is more than 7 s, there is a possibility of improvement as much as carbon is reduced. However, there is a limit to effuse through the reaction with carbon, and the improvement effect is expected to be saturated as carbon is reduced.
To apply Al 2 O 3 as a passivation dielectric film, the quality of the interface region between Si and Al 2 O 3 is crucial. Carbon in Al 2 O 3 acts as an interface trap in the interface region between the Al 2 O 3 dielectric and Si substrate [21]. The parallel conductance versus frequency plots of the Al 2 O 3 films with various D it values are shown in Figure 6. D it was measured using the conductance method [13]. The D it of the S1_as_dep sample was 8.98 × 10 13 eV −1 ·cm −2 , whereas that of the S2_as_dep sample was 1.12 × 10 12 eV −1 ·cm −2 . The interface traps of the S2 sample decreased with a decrease in the carbon impurity content in the interface area with increasing O 2 plasma exposure time. After PMA, the interface region between the Al 2 O 3 dielectric and Si was improved due to various reasons. First, an IL was formed after the application of PMA to the Al 2 O 3 gate stack. Therefore, the number of hydroxyl groups is reduced, thereby decreasing the number of interface traps [22]. For other reason, as crystallization of Al 2 O 3 occurred due to PMA, defects and dangling bonds acting as traps in the interface region were removed. In addition, crystallization of the Al 2 O 3 dielectric stabilized the bond between the Al 2 O 3 and Si substrate [10].
The decrease in the carbon impurity content with increasing O2 plasma exposure time was validated using SIMS depth profiling. As shown in Figure 5, the amount of carbon impurities in the Al2O3 film deposited with an O2 plasma exposure time of 7 s is considerably less than that of the Al2O3 sample deposited with a shorter O2 plasma exposure time. As the O2 plasma exposure time increased, more carbon was effused into the COX (x = 1-2) gas state through numerous reactions between the oxygen plasma and carbon [16]. If the O2 plasma exposure time is more than 7 s, there is a possibility of improvement as much as carbon is reduced. However, there is a limit to effuse through the reaction with carbon, and the improvement effect is expected to be saturated as carbon is reduced. To apply Al2O3 as a passivation dielectric film, the quality of the interface region between Si and Al2O3 is crucial. Carbon in Al2O3 acts as an interface trap in the interface region between the Al2O3 dielectric and Si substrate [21]. The parallel conductance versus frequency plots of the Al2O3 films with various Dit values are shown in Figure 6. Dit was measured using the conductance method [13]. The Dit of the S1_as_dep sample was 8.98 × 10 13 eV −1 ·cm −2 , whereas that of the S2_as_dep sample was 1.12 × 10 12 eV −1 ·cm −2 . The interface traps of the S2 sample decreased with a decrease in the carbon impurity content in the interface area with increasing O2 plasma exposure time. After PMA, the interface region between the Al2O3 dielectric and Si was improved due to various reasons. First, an IL was formed after the application of PMA to the Al2O3 gate stack. Therefore, the number of hydroxyl groups is reduced, thereby decreasing the number of interface traps [22]. For other reason, as crystallization of Al2O3 occurred due to PMA, defects and dangling bonds acting as traps in the interface region were removed. In addition, crystallization of the Al2O3 dielectric stabilized the bond between the Al2O3 and Si substrate [10]. In summary, the number of interface traps of the S2_PMA sample, in which the concentrations of both carbon impurities and hydroxyl groups were reduced, were the lowest in this study (Dit = 1.35 × 10 11 eV −1 ·cm −2 ).
The interface improvement owing to the increase in the O2 plasma exposure time was also validated using the breakdown characteristics. The gate leakage current with an increase in the electrical field of the S1 and S2 Al2O3 samples is shown in Figure 7a. In the case of S1_as_dep, the breakdown occurred at 9.73 MV/cm. The breakdown characteristics improved after PMA was performed owing to the formation of an IL, which occurred at 11.47 MV/cm. However, breakdown did not occur until the application of the maximum electric field (14 MV/cm) of the 4200-SCS equipment in the case of the S2 sample. Furthermore, breakdown did not occur in the case of the S2_as_dep sample without the IL. This was because of the reduction in the impurity content in the interface area with an increase in the O2 plasma exposure time.  In summary, the number of interface traps of the S2_PMA sample, in which the concentrations of both carbon impurities and hydroxyl groups were reduced, were the lowest in this study (D it = 1.35 × 10 11 eV −1 ·cm −2 ).
The interface improvement owing to the increase in the O 2 plasma exposure time was also validated using the breakdown characteristics. The gate leakage current with an increase in the electrical field of the S1 and S2 Al 2 O 3 samples is shown in Figure 7a. In the case of S1_as_dep, the breakdown occurred at 9.73 MV/cm. The breakdown characteristics improved after PMA was performed owing to the formation of an IL, which occurred at 11.47 MV/cm. However, breakdown did not occur until the application of the maximum electric field (14 MV/cm) of the 4200-SCS equipment in the case of the S2 sample. Furthermore, breakdown did not occur in the case of the S2_as_dep sample without the IL. This was because of the reduction in the impurity content in the interface area with an increase in the O 2 plasma exposure time.
improved after PMA was performed owing to the formation of an IL, which occurred at 11.47 MV/cm. However, breakdown did not occur until the application of the maximum electric field (14 MV/cm) of the 4200-SCS equipment in the case of the S2 sample. Furthermore, breakdown did not occur in the case of the S2_as_dep sample without the IL. This was because of the reduction in the impurity content in the interface area with an increase in the O2 plasma exposure time.  In addition, the FN plots to validate the improvement in the interface quality are shown in Figure 7b. The FN plot is analyzed using the leakage current density caused by FN tunneling, J FN , and can be described as follows: where where A is the Richardson's constant; q is the electronic charge; h is Planck's constant; m 0 is the free electron mass; m * is the effective electron mass in the oxide; and Φ B is the barrier height [23]. The steeper the slope in the FN plot, the larger the FN barrier height Φ B [4].
Since the absolute value of the slope of the S2_as_dep sample (slope = −182.06) is larger than that of the S1_as_dep sample (slope = −103.28), it means that the barrier height is higher in S2_as_dep. Therefore, the FN plot shows that the interface region of Al 2 O 3 /Si was improved in the S2 sample with increased O 2 plasma exposure time.
In summary, the increase in the O 2 plasma exposure time decreases the carbon content in Al 2 O 3 , which reduces D it , improves the breakdown field, and prevents the V fb shift. However, the H 2 plasma treatment decreased the quality of the oxide and interface owing to the increase in the O 2 plasma exposure time, which is discussed later.

H 2 Plasma Treatment
H 2 plasma treatment significantly decreased the carbon impurity content in Al 2 O 3 in previous studies [10], thereby preventing the V fb shift and improving the breakdown characteristics. However, further improvements in the interface quality is required for next-generation CIS devices. Therefore, we analyzed the effects of the H 2 plasma treatment on Al 2 O 3 films with increasing O 2 plasma exposure time.
D it values depending on various treatments on the Al 2 O 3 samples are shown in Figure 8.
The average D it of the sample with the H 2 plasma treatment was 4.45 × 10 12 eV −1 ·cm −2 , which was significantly smaller than that of as-deposited S1. However, the average D it of the sample with the H 2 plasma treatment was 1.13 × 10 12 eV −1 ·cm −2 in the case of S2 samples with an increased O 2 plasma exposure time, which increased compared with the average D it of as-deposited S2 (D it,as_dep S2 = 5.79 × 10 11 eV −1 ·cm −2 ). A similar trend was observed after PMA. D it was higher in the S2 sample with the H 2 plasma treatment and PMA than that of the S2 sample treated with only PMA.
Al2O3 films with increasing O2 plasma exposure time.
Dit values depending on various treatments on the Al2O3 samples are shown in Figure  8. The average Dit of the sample with the H2 plasma treatment was 4.45 × 10 12 eV −1 ·cm −2 , which was significantly smaller than that of as-deposited S1. However, the average Dit of the sample with the H2 plasma treatment was 1.13 × 10 12 eV −1 ·cm −2 in the case of S2 samples with an increased O2 plasma exposure time, which increased compared with the average Dit of as-deposited S2 (Dit,as_dep S2 = 5.79 × 10 11 eV −1 ·cm −2 ). A similar trend was observed after PMA. Dit was higher in the S2 sample with the H2 plasma treatment and PMA than that of the S2 sample treated with only PMA. A large amount of carbon impurities was removed owing to the increased O 2 plasma exposure time in the S2 sample. Therefore, there are not enough carbon impurities for the reaction with the H 2 plasma. As a result, owing to the excessive postprocessing H 2 plasma treatment on the S2 sample, H impurities remained inside the Al 2 O 3 film [24]. In addition, additional H 2 plasma treatment for carbon impurities, whose content was reduced owing to an increase in the O 2 plasma exposure time, had a more significant effect on the formation of defects owing to damage due to the plasma treatment compared with the effects of curing defects owing to carbon content reduction [25]. In conclusion, in the case of the S2 sample with increased O 2 plasma exposure time, excessive postprocessing H 2 plasma treatment caused residual H impurities and plasma damage, which contributed to increase D it by forming dangling bonds in interface region.
Using the capacitance vs. voltage curve, the plasma damage to the gate stack was confirmed. The normalized capacitance before and after the H 2 plasma treatment in the S2 sample with an increased O 2 plasma exposure time is shown in Figure 9. In contrast to the S2_as_dep sample, the C-V hump occurs near V fb in the S2_H 2 plasma sample. Therefore, the hydrogen plasma, which should be effused via the reaction with carbon, damaged the Al 2 O 3 dielectric.
The formation of defects in the oxide and interface regions of the S2 sample owing to the H 2 plasma treatment resulted in more leakage flow in the gate stack. In contrast to the S2_as_dep sample, where breakdown does not occur even under the electric field limit of the 4200-SCS equipment (E field = 14 MV/cm), the breakdown occurs at 11.2 MV/cm in the S2_H 2 plasma sample ( Figure 10). As a result, in the case of the Al 2 O 3 film with increased O 2 plasma exposure time, H 2 plasma treatment rather deteriorates the interface quality between Al 2 O 3 dielectric and Si.
In summary, H 2 plasma treatment has different effects depending on the O 2 plasma exposure time during deposition of the Al 2 O 3 dielectric. H 2 plasma treatment was effective for S1 samples with a large amount of carbon impurities because of the short O 2 plasma exposure time. Due to the reduction of carbon impurities, the D it of the S1 sample was greatly reduced after H 2 plasma treatment. However, the treatment effects on S2 samples was rather poor, resulting in reduced carbon content owing to the long O 2 plasma exposure time. H 2 plasma treatment produced residual H impurities in the S2 samples and also caused plasma damage. Therefore, H 2 plasma treatment rather increased D it in the Al 2 O 3 with increased O 2 plasma exposure time.
Using the capacitance vs. voltage curve, the plasma damage to the gate stack was confirmed. The normalized capacitance before and after the H2 plasma treatment in the S2 sample with an increased O2 plasma exposure time is shown in Figure 9. In contrast to the S2_as_dep sample, the C-V hump occurs near Vfb in the S2_H2 plasma sample. Therefore, the hydrogen plasma, which should be effused via the reaction with carbon, damaged the Al2O3 dielectric. The formation of defects in the oxide and interface regions of the S2 sample owing to the H2 plasma treatment resulted in more leakage flow in the gate stack. In contrast to the S2_as_dep sample, where breakdown does not occur even under the electric field limit of the 4200-SCS equipment (Efield = 14 MV/cm), the breakdown occurs at 11.2 MV/cm in the S2_H2 plasma sample ( Figure 10). As a result, in the case of the Al2O3 film with increased O2 plasma exposure time, H2 plasma treatment rather deteriorates the interface quality between Al2O3 dielectric and Si. In summary, H2 plasma treatment has different effects depending on the O2 plasma exposure time during deposition of the Al2O3 dielectric. H2 plasma treatment was effective for S1 samples with a large amount of carbon impurities because of the short O2 plasma exposure time. Due to the reduction of carbon impurities, the Dit of the S1 sample was greatly reduced after H2 plasma treatment. However, the treatment effects on S2 samples was rather poor, resulting in reduced carbon content owing to the long O2 plasma exposure time. H2 plasma treatment produced residual H impurities in the S2 samples and also caused plasma damage. Therefore, H2 plasma treatment rather increased Dit in the Al2O3 with increased O2 plasma exposure time.

Conclusions
The criterion of fixed charges in the Al2O3 film for application as a CIS passivation layer was satisfied in a previous study; however, the issue of interface traps remained unresolved. Further improvement in the interface area is required for Al2O3 to be used as a passivation dielectric layer. Therefore, this study investigated the conditions to reduce defect contents and the Dit of the Al2O3 film. The carbon content inside the Al2O3 was significantly decreased by adjusting the O2 plasma exposure time to induce more reactions during dielectric deposition. Dit was significantly decreased owing to the reduction in the amount of carbon impurities, and the improvement in the interface region was validated using the breakdown characteristics. Moreover, H2 plasma treatment effectively reduced

Conclusions
The criterion of fixed charges in the Al 2 O 3 film for application as a CIS passivation layer was satisfied in a previous study; however, the issue of interface traps remained unresolved. Further improvement in the interface area is required for Al 2 O 3 to be used as a passivation dielectric layer. Therefore, this study investigated the conditions to reduce defect contents and the D it of the Al 2 O 3 film. The carbon content inside the Al 2 O 3 was significantly decreased by adjusting the O 2 plasma exposure time to induce more reactions during dielectric deposition. D it was significantly decreased owing to the reduction in the amount of carbon impurities, and the improvement in the interface region was validated using the breakdown characteristics. Moreover, H 2 plasma treatment effectively reduced D it in Al 2 O 3 films with a short O 2 plasma exposure time during deposition. However, H 2 plasma treatment of the Al 2 O 3 film deposited with a long O 2 plasma exposure time rather increased D it due to plasma damage. PMA slightly decreased the permittivity after Al 2 O 3 deposition; however, D it significantly decreased. In particular, in the case of Al 2 O 3 samples with increased O 2 plasma exposure time, after PMA, it had the lowest D it , which is suitable for use as a passivation layer for CIS.